<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<style>
  .box {
    color: rebeccapurple;
  }

  .actvie {
    color: aquamarine;
    font-size: large;
  }
</style> 

<body>
  <div class="box actvie">文字</div>
</body>
<script>
  const box = document.querySelector('.box');
  //box.classList.add('actvie')
  //box.classList.remove('actvie')
  box.classList.toggle('actvie')
</script>

</html>